lsqcurvefit help

I am absolutely new to MATLAB. I have 15 data sets and want to do a curve fitting to extract some parameters. Seems lsqcurvefit can do the job. First I tried to run the lsqcurvefit example in MATLAB. I copy and paste the code from the help file to a .m file like this:

function F = myfun(x,xdata)

F = x(1)*exp(x(2)*xdata);

% Assume you determined xdata and ydata experimentally

xdata = [0.9 1.5 13.8 19.8 24.1 28.2 35.2 60.3 74.6 81.3];

ydata = [455.2 428.6 124.1 67.3 43.2 28.1 13.1 -0.4 -1.3 -1.5];

x0 = [100; -1];

[x] = lsqcurvefit(@myfun,x0,xdata,ydata);

When I trie to run the code, it says something like this in the command windows:

??? Input argument "x" is undefined.

Error in ==> test1 at 3 F = x(1)*exp(x(2)*xdata);

What do I miss here? I know I need to get a book to study MATLAB. But I need to solve the problem as soon as possible. Thanks for help.

Answer 1

[Andrew Newell]

Maybe you have all of the code in one file? The function myfun should be in a separate file. Or you could use an anonymous function:

myfun = @(x,xdata) x(1)*exp(x(2)*xdata);

% Assume you determined xdata and ydata experimentally

xdata = [0.9 1.5 13.8 19.8 24.1 28.2 35.2 60.3 74.6 81.3];

ydata = [455.2 428.6 124.1 67.3 43.2 28.1 13.1 -0.4 -1.3 -1.5];

x0 = [100; -1];

[x] = lsqcurvefit(myfun,x0,xdata,ydata);

[zhengz]

You are the man! I tried both ways. They all work.

Answer 2

[MUMATZ QURESHI]

function myfun

xdata = [0.9 1.5 13.8 19.8 24.1 28.2 35.2 60.3 74.6 81.3];

ydata = [455.2 428.6 124.1 67.3 43.2 28.1 13.1 -0.4 -1.3 -1.5];

x0 = [100, -1]; % Starting guess

x = lsqcurvefit(@myfun1,x0,xdata,ydata)

times = linspace(xdata(1),xdata(end));

figure;plot(xdata,ydata,'ko',times,myfun1(x,times),'b-')

legend('Data','Fitted exponential')

title('Data and Fitted Curve')

end

function F = myfun1(x,xdata)

F= x(1).*exp(x(2).*xdata);

end

Answer 3

[Milad]

Solved mine to, thanks

Answer 4

[Daniela Garza Niño de Rivera]

my code is not working is says :

" Error in Problem5M2>FunToFitM2 (line 12)

A=p(1);B=p(2);C=p(3);D=p(4);

Error in lsqcurvefit (line 213)

initVals.F = feval(funfcn_x_xdata{3},xCurrent,XDATA,varargin{:});

Error in Problem5M2 (line 6)

[P]=lsqcurvefit(@FunToFitM2,P0,T,muP);

Caused by:

Failure in initial objective function evaluation. LSQCURVEFIT cannot continue.

>> ""

how can i fix it?

here is the code:

function[P]=Problem5M2()

V= [275,10.52;277.2,8.702;279.4,6.887;281.7,5.071;283.9,3.705;286.1,3.164;288.3,2.603;290.6,2.053;292.8,1.502;295,1.306];

T=V(:,1); muP=V(:,2);

P0=[1;1];

[P]=lsqcurvefit(@FunToFitM2,P0,T,muP);

A=P(1);B=P(2);C=P(3);D=P(4);

P2=[A;B;C;D];

end

function[muP]=FunToFitM2(p,T)

A=p(1);B=p(2);C=p(3);D=p(4);

muP=(10).^(A+B./(T+C)+(D.*(T)));

end